As eye movement desensitization and reprocessing (EMDR) has been increasingly applied in complex trauma-related disorders, including complex dissociative disorders, and trauma-related borderline personality disorder, EMDR practice may benefit from theories developed to account for the
dissociative nature of these disorders, such as the theory of structural dissociation of the personality (TSDP). TSDP postulates that the personality of traumatized individuals is unduly divided in two basic types of dissociative subsystems or parts. One type involves dissociative parts primarily
mediated by daily life action systems or motivational systems. The other type involves dissociative parts, fixated in traumatic memories, primarily mediated by the defense action system. The more severe and chronic the traumatization, the more dissociative parts can be expected to exist. This
article presents the basics of TSDP, and a second article will provide guidelines for the treatment of complex trauma-related disorders based on this theory.

The Journal of EMDR Practice and Research is a quarterly, peer-reviewed publication devoted to integrative, state-of-the-art papers about Eye Movement Desensitization and Reprocessing. It is a broadly conceived interdisciplinary journal that stimulates and communicates research and theory about EMDR, and their application to clinical practice.